Globally, the annual death rate from RSV is estimated at more than 160,000 and the clinical burden of RSV infection is comparable to that of influenza (Bourgeois et al., 2009; Boyce et al., 2000; Hall et al., 2009; Stockman et al., 2012). The epidemic season for RSV runs from late fall through early spring. The primary populations at risk for poor outcome are children below 5 years of age, immunocompromised patients and older adults, particularly those who are institutionalized or have chronic underlying disease (Hall et al., 2009; Falsey et al., 2005). There is generally no available therapy for RSV infection, except for supportive care. Few drugs exist and fewer have been approved for therapeutic use (WO 2002/026228; WO 2002/062290; WO 2001/095910; WO 2012/080451). Inhaled ribavirin is approved for the treatment of laboratory-diagnosed RSV infection but is administered only to some bone marrow transplant and immunocompromised patients, because of its limited effectiveness, complexity of administration and mutagenicity potential for patients and staff. Because of the absence of effective therapy for RSV infections and the significance of RSV morbidity and/or morality in at-risk populations, the introduction of an effective RSV agent will be considered a major breakthrough in the care of these patients.